Directional microphone assembly

ABSTRACT

A directional microphone assembly for a hearing aid is disclosed. The hearing aid has one or more microphone cartridge(s), and first and second sound passages. Inlets to the sound passages, or the sound passages themselves, are spaced apart such that the shortest distance between them is less than or approximately equal to the length of the microphone cartridge(s). A sound duct and at least one surface of a microphone cartridge may form each sound passage, where the sound duct is mounted with the microphone cartridge. Alternatively, each sound duct may be formed as an integral part of a microphone cartridge.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application makes reference to and claims priority to and thebenefit of U.S. Non-Provisional patent application Ser. No. 09/973,078filed on Oct. 5, 2001, which in turn claims priority to U.S. ProvisionalPatent Application Ser. No. 60/237,988 filed Oct. 5, 2000 and herebyincorporates herein by reference the respective entireties thereof.

This application also makes reference to and claims priority to and thebenefit of U.S. Non-Provisional patent application Ser. No. 09/565,262filed on May 5, 2000, which is a continuation-in-part of U.S.Non-Provisional patent application Ser. No. 09/252,572 filed Feb. 18,1999, which is a continuation-in-part of U.S. Non-Provisional patentapplication Ser. No. 08/775,139 filed Dec. 31, 1996 now U.S. Pat. No.5,878,147 issued Mar. 2, 1999 and hereby incorporates herein byreference the respective entireties thereof.

This application also hereby incorporates herein by reference U.S.Provisional Patent Application Ser. No. 60/237,988, U.S. Pat. No.5,878,147, and U.S. Pat. No. 5,524,056 in their respective entireties.

BACKGROUND OF THE INVENTION

The application of directional microphones to hearing aids is well knownin the patent literature (Wittkowski, U.S. Pat. No. 3,662,124 dated1972; Knowles and Carlson, U.S. Pat. No. 3,770,911 dated 1973; Killion,U.S. Pat. No. 3,835,263 dated 1974; Ribic, U.S. Pat. No. 5,214,709, andKillion et al. U.S. Pat. No. 5,524,056, 1996) as well as commercialpractice (Maico hearing aid model MC033, Qualitone hearing aid modelTKSAD, Phonak “AudioZoom” hearing aid, and others).

Directional microphones are used in hearing aids to make it possible forthose with impaired hearing to carry on a normal conversation at socialgatherings and in other noisy environments. As hearing loss progresses,individuals require greater and greater signal-to-noise ratios in orderto understand speech. Extensive digital signal processing research hasresulted in the universal finding that nothing can be done with signalprocessing alone to improve the intelligibility of a signal in noise,certainly in the common case where the signal is one person talking andthe noise is other people talking. There is at present no practical wayto communicate to the digital processor that the listener now wishes toturn his attention from one talker to another, thereby reversing theroles of signal and noise sources.

It is important to recognize that substantial advances have been made inthe last decade in the hearing aid art to help those with hearing losshear better in noise. Available research indicates, however, that theadvances amounted to eliminating defects in the hearing aid processing,defects such as distortion, limited bandwidth, peaks in the frequencyresponse, and improper automatic gain control or AGC action. Researchconducted in the 1970's, before these defects were corrected, indicatedthat the wearer of hearing aids typically experienced an additionaldeficit of 5 to 10 dB above the unaided condition in the signal-to-noiseratio (“S/N”) required to understand speech. Normal hearing individualswearing those same hearing aids might also experience a 5 to 10 dBdeficit in the S/N required to carry on a conversation, indicating thatit was indeed the hearing aids that were at fault. These problems werediscussed by Applicant Killion in a recent paper “Why some hearing aidsdon't work well!!!” (Hearing Review, January 1994, pp. 40-42).

Recent data obtained by the Applicants confirm that hearing impairedindividuals need an increased signal-to-noise ratio even when no defectsin the hearing aid processing exist. As measured on one popularspeech-in-noise test, the SIN test, those with mild loss typically needsome 2 to 3 dB greater S/N than those with normal hearing; those withmoderate loss typically need 5 to 7 dB greater S/N; those with severeloss typically need 9 to 12 dB greater S/N. These figures were obtainedunder conditions corresponding to defect free hearing aids.

As described below, a headworn first-order directional microphone canprovide at least a 3 to 4 dB improvement in signal-to-noise ratiocompared to the open ear, and substantially more in special cases. Thisdegree of improvement will bring those with mild hearing loss back tonormal hearing ability in noise, and substantially reduce the difficultythose with moderate loss experience in noise. In contrast, traditionalomnidirectional head-worn microphones cause a signal-to-noise deficit ofabout 1 dB compared to the open ear, a deficit due to the effects ofhead diffraction and not any particular hearing aid defect.

A little noticed advantage of directional microphones is their abilityto reduce whistling caused by feedback (Knowles and Carlson, 1973, U.S.Pat. No. 3,770,911). If the ear-mold itself is well fitted, so that thevent outlet is the principal source of feedback sound, then therelationship between the vent and the microphone may sometimes beadjusted to reduce the feedback pickup by 10 or 20 dB. Similarly, thehigher-performance directional microphones have a relatively low pickupto the side at high frequencies, so the feedback sound caused byfaceplate vibration will see a lower microphone sensitivity than soundscoming from the front.

Despite these many advantages, the application of directionalmicrophones has been restricted to only a small fraction ofBehind-The-Ear (BTE) hearing aids, and only rarely to the much morepopular In-The-Ear (ITE) hearing aids which presently comprise some 80%of all hearing aid sales.

Part of the reason for this low usage was discovered by Madafarri, whomeasured the diffraction about the ear and head. He found that for thesame spacing between the two inlet ports of a simple first-orderdirectional microphone, the ITE location produced only half themicrophone sensitivity. Madafarri found that the diffraction of soundaround the head and ear caused the effective port spacing to be reducedto about 0.7 times the physical spacing in the ITE location, while itwas increased to about 1.4 times the physical spacing in the BTElocation. In addition to a 2:1 sensitivity penalty for the same portspacing, the constraints of ITE hearing aid construction typicallyrequire a much smaller port spacing, further reducing sensitivity.

Another part of the reason for the low usage of directional microphonesin ITE applications is the difficulty of providing the front and rearsound inlets plus a microphone cartridge in the space available. Asshown in FIG. 17 of the '056 patent mentioned above, the prior art usesat least one metal inlet tube (often referred to as a nipple) welded tothe side of the microphone cartridge and a coupling tube between themicrophone cartridge and the faceplate of the hearing aid. Thearrangement of FIG. 17 of the '056 patent wherein the microphonecartridge is also parallel with the faceplate of the hearing aide forcesa spacing D as shown in that figure which may not be suitable for allears.

A further problem is that of obtaining good directivity acrossfrequency. Extensive experiments conducted by Madafarri as well as bythe Applicants over the last 25 years have shown that in order to obtaingood directivity across the audio frequencies in a head-worn directionalmicrophone it, requires great care and a good understanding of theoperation of sound in tubes (as described, for example, by Zuercher,Carlson, and Killion in their paper “Small acoustic tubes,” J. Acoust.Soc. Am., V. 83, pp. 1653-1660, 1988).

A still further problem with the application of directional microphonesto hearing aids is that of microphone noise. Under normal conditions,the noise of a typical non-directional hearing aid microphone cartridgeis relatively unimportant to the overall performance of a hearing aid.Sound field tests show that hearing aid wearers can often detect toneswithin the range of 0 to 5 dB Hearing Level, i.e., within 5 dB ofaverage young normal listeners and well within the accepted 0 to 20 dBlimits of normal hearing. But when the same microphone cartridges areused to form directional microphones, a low frequency noise problemarises. The subtraction process required in first-order directionalmicrophones results in a frequency response falling at 6 dB/octavetoward low frequencies. As a result, at a frequency of 200 Hz, thesensitivity of a directional microphone may be 30 dB below thesensitivity of the same microphone cartridge operated in anomnidirectional mode.

When an equalization amplifier is used to correct the directionalmicrophone frequency response for its low frequency drop in sensitivity,the amplifier also amplifies the low frequency noise of the microphone.In a reasonably quiet room, the amplified low frequency microphone noisemay now become objectionable. Moreover, with or without equalization,the masking of the microphone noise will degrade the best aided soundfield threshold at 200 Hz to approximately 35 dB HL, approaching the 40dB HL lower limits for what is considered a moderate hearing impairment.

The equalization amplifier itself also adds to the complication of thehearing aid circuit. Thus, even in the few cases where ITE aids withdirectional microphones have been available, to applicant's knowledge,their frequency response has never been equalized. For this reason,Killion et al (U.S. Pat. No. 5,524,056) recommend a combination of aconventional omnidirectional microphone and a directional microphone sothat the lower internal noise omnidirectional microphone may be chosenduring quiet periods while the external noise rejecting directionalmicrophone may be chosen during noisy periods.

Although directional microphones appear to be the only practical way tosolve the problem of hearing in noise for the hearing-impairedindividual, they have been seldom used even after nearly three decadesof availability. It is the purpose of the present invention to providean improved and fully practical directional microphone for ITE hearingaids.

Before summarizing the invention, a review of some further backgroundinformation will be useful. Since the 1930s, the standard measure ofperformance in directional microphones has been the “directivity index”or DI, the ratio of the on-axis sensitivity of the directionalmicrophone (sound directly in front) to that in a diffuse field (soundcoming with equal probability from all directions, sometimes calledrandom incidence sound). The majority of the sound energy at thelistener's eardrum in a typical room is reflected, with the direct soundoften less than 10% of the energy. In this situation, the direct pathinterference from a noise source located at the rear of a listener maybe rejected by as much as 30 dB by a good directional microphone, butthe sound reflected from the wall in front of the listener willobviously arrive from the front where the directional microphone has(intentionally) good sensitivity. If all of the reflected noise energywere to arrive from the front, the directional microphone could nothelp.

Fortunately, the reflections for both the desired and undesired soundstend to be more or less random, so the energy is spread out over manyarrival angles. The difference between the “random incidence” or“diffuse field” sensitivity of the microphone and its on-axissensitivity gives a good estimate of how much help the directionalmicrophone can give in difficult situations. An additional refinementcan be made where speech intelligibility is concerned by weighing thedirectivity index at each frequency to the weighing function of theArticulation Index as described, for example, by Killion and Mueller onpage 2 of The Hearing Journal, Vol. 43, Number 9, September 1990. Table1 gives one set of weighing values suitable for estimating theequivalent overall improvement in signal-to-noise ratio as perceived bysomeone trying to understand speech in noise.

The directivity index (DI) of the two classic, first-order directionalmicrophones, the “cosine” and “cardioid” microphones, is 4.8 dB. In thefirst case the microphone employs no internal acoustic time delaybetween the signals at the two inlets, providing a symmetrical figure 8pattern. The cardioid employs a time delay exactly equal to the time ittakes on-axis sound to travel between the two inlets. Compared to thecosine microphone, the cardioid has twice the sensitivity for sound fromthe front and zero sensitivity for sound from the rear. A furtherincrease in directivity performance can be obtained by reducing theinternal time delay. The hypercardioid, with minimum sensitivity forsound at 110 degrees from the front, has a DI of 6 dB. The presence ofhead diffraction complicates the problem of directional microphonedesign. For example, the directivity index for an omni BTE or ITEmicrophone is −1.0 to −2.0 dB at 500 and 1000 Hz.

Recognizing the problem of providing good directional microphoneperformance in a headworn ITE hearing aid application, applicant's setabout to discover improved means and methods of such application. It isreadily understood that the same solutions that make an ITE applicationpractical can be easily applied to BTE applications as well.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present invention may be found in a hearing aid havingone or more microphone cartridge(s). The hearing aid also has a firstsound passage that couples sound energy to a first sound port of one ofthe microphone cartridge(s), and a second sound passage that couplessound energy to a second sound port of one of the microphonecartridge(s). The longest distance between first and second sound inletsof the first and second sound passages, respectively, is less than orapproximately equal to the sum of the length of the microphonecartridge(s), the diameter of the first sound inlet and the diameter ofthe second sound inlet. The longest distance may be, for example, lessthan approximately 0.258 inches, such as 0.215 inches for example.

The diameters of the first and second sound inlets may be approximatelyequal, for example. The first and second sound inlets may have, forexample, a center to center spacing of less than approximately 0.2inches, such as approximately 0.157 inches, for example.

In another embodiment, the hearing aid has one or more microphonecartridge(s), and first and second sound ducts. The microphonecartridge(s) have first and second ports located, respectively, on firstand second outer surfaces of the microphone cartridge(s). The first andsecond sound ducts likewise have, respectively, first and second innersurfaces. The first sound duct is operatively coupled to at least thefirst outer surface of a microphone cartridge, and the second sound ductis operatively coupled to at least the second outer surface of, forexample, the same microphone cartridge (or a different microphonecartridge in the case of two or more microphone cartridges). The innersurface of the first sound duct and at least the first outer surface ofthe microphone cartridge create a volume representative of a first soundpassage to the first port, and the inner surface of the second soundduct and at least the second outer surface of the microphone cartridgecreate a volume representative of a second sound passage to the secondport.

In a further embodiment the hearing aid has one or more microphonecartridges, a first sound passage communicating with a microphonecartridge, and a second sound passage communicating with, for example,the same microphone cartridge (or a different microphone cartridge inthe case of a two or more microphone cartridges). The shortest distancebetween the first and second sound passages is less than orapproximately equal to the length of the one or more microphonecartridges. Such distance may be, for example, less than approximately0.142 inches, such as 0.092 inches, for example.

In still a further embodiment, the hearing aid has a housing with anouter surface, such as formed by a faceplate for example, which in turnhas first and second sound inlets. First and second sound passagescouple sound energy from, respectively, the first and second soundinlets to, respectively, a microphone cartridge (or to separatemicrophone cartridges in the case of two or more microphone cartridges).The shortest distance between the first and second sound inlets may be,for example, less than or approximately equal to the length of the oneor more microphone cartridges. Again, such distance may be, for example,less than approximately 0.142 inches, such as 0.092 inches, for example.

In the above embodiments, the first and second sound passages may beformed by, respectively, first and second sound ducts, where the firstand second sound ducts are mounted with the microphone cartridge(s).Alternatively, the sound ducts may be formed as integral portions of themicrophone cartridge(s). In addition, the sound passages may be formedin whole or in part in a housing portion, such as a faceplate forexample, of the hearing aid.

The hearing aid may be, for example, an in-the-ear hearing aid or abehind-the-ear hearing aid, and the microphone cartridge(s) may be, forexample, a directional cartridge in the case of a single cartridgedesign, or more than one omnidirectional cartridge (or some combinationof directional and omnidirectional cartridges, in the case of a multiplecartridge design).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of one embodiment of a directionalmicrophone assembly in accordance with the present invention.

FIG. 2 is a top view of the directional microphone assembly of FIG. 1.

FIG. 3 is a top view of the directional microphone assembly of FIG. 1showing a restrictor placed in a top portion of a (front) sound duct.

FIG. 4 is a top view of the directional microphone assembly of FIG. 1showing acoustic dampers placed in top portions of sound ducts.

FIG. 5 is a side view of the directional microphone assembly of FIG. 1showing both the restrictor and the acoustic dampers and in an assembledrelationship.

FIG. 6 illustrates one embodiment of directional microphone cartridge ofthe directional microphone assembly of the present invention.

FIG. 7 illustrates one embodiment of a sound duct in accordance with thepresent invention.

FIG. 8 illustrates additional detail regarding the mounting of the soundduct of FIG. 7 on a directional microphone cartridge.

FIG. 9 illustrates another embodiment of a sound duct in accordance withthe present invention.

FIG. 10 illustrates additional detail regarding the mounting of thesound duct of FIG. 9 on a directional microphone cartridge.

FIG. 11 illustrates a directional microphone cartridge housing portionhaving sound duct portions formed as an integral part of the housingportion.

FIG. 12 illustrates another directional microphone cartridge housingportion having sound duct portions formed as an integral part of thehousing portion.

FIG. 13 illustrates an assembly technique for the housing portions ofFIGS. 11 and 12.

FIG. 14 illustrates a completed assembly, in which the housing portionsif FIGS. 11 and 12 are engaged to form a complete directional microphonecartridge having integrated sound ducts.

FIG. 15 illustrates an alternate embodiment of a directional microphoneassembly of the present invention.

FIG. 16 is another view of the directional microphone assembly of FIG.15.

FIG. 17 illustrates a directional microphone assembly of the presentinvention having an equalization hybrid.

FIGS. 18A and 18B show exemplary details of the equalization hybrid ofFIG. 17.

FIG. 19 is a diagram illustrating an exemplary interconnection betweenthe directional microphone cartridge and the equalization hybrid of FIG.17.

FIG. 20 is a circuit diagram illustrating exemplary circuitry forimplementing equalization.

FIG. 21 illustrates a directional microphone cartridge having a largerhousing volume to accommodate internal equalization circuitry.

FIGS. 22 and 23 are side and perspective views, respectively, of adirectional microphone assembly having internal equalization circuitry.

FIG. 24 illustrates an in-the-ear hearing aid having a directionalmicrophone assembly mounted therein.

FIG. 25 is an exploded view of the directional microphone assembly ofFIGS. 11-14, illustrating the internal components as well as thecartridge portions.

FIGS. 26A-G collectively illustrate a component by component assemblytechnique for the directional microphone assembly of FIGS. 11-14, usingthe components set forth in FIG. 25.

FIGS. 27A-G respectively illustrate the individual components set forthin FIG. 25.

FIG. 28 is a top view of an alternate embodiment of the directionalmicrophone assembly of the present invention, in which the sound ductsare offset from each other and relative to the center of the casehousing.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a side view of one embodiment of a directionalmicrophone assembly in accordance with the present invention.Directional microphone assembly 101 comprises a directional microphonecartridge 103 and sound ducts or tubes 105 and 107. Directionalmicrophone cartridge 103 may have a height dimension of onlyapproximately 0.142 inches (3.60 mm) and a length dimension of onlyapproximately 0.142 inches (3.60 mm), for example, a shown in FIG. 1.Directional microphone cartridge 103 may be made from a Knowles™ 4568cartridge or a Microtronics 6368, for example. Of course, directionalmicrophone cartridge 103 may have other dimensions, and may be made fromother types of cartridges, than those specifically listed.

Sound ducts 105 and 107 form front and rear sound inlet passages,respectively, for coupling of sound energy from the sound field to thedirectional microphone cartridge 103. Sound duct 105 has a port or inlet109 that may have an inner diameter of 0.050 inches (1.27 mm) and anouter diameter of 0.058 inches (1.47 mm), for example. Sound duct 107has a similar port or inlet 111, which may have the same dimensions asport 109. The center of inlet 109 may be spaced apart a distance of0.157 inches (4.00 mm), for example, from the center of inlet 111, asshown in FIG. 1.

Also, as can be seen from FIG. 1, sound ducts 105 and 107 may be mountedwith directional microphone cartridge 103 such that portions 113 and 115of the directional microphone cartridge 103 extend partially into soundducts 105 and 107, respectively (as explained more completely below). Inaddition, each of sound ducts 105 and 107 may extend only 0.040 inches(1.02 mm), for example, above a top surface 117 of the directionalmicrophone cartridge 103. Given the configuration shown in FIG. 1,therefore, the overall longest (i.e., length) dimension of the totaldirectional microphone assembly 103 may be approximately 0.215 inches(5.47 mm) or less. This length is shorter than the total length obtainedby combining the length of the directional microphone cartridge 103 withthe diameter dimensions of both the inlet ports 109 and 111. Thedirectional microphone assembly 103 may also have a height dimension ofapproximately 0.182 inches (4.62 mm) or less.

FIG. 2 is a top view of the directional microphone assembly 101 ofFIG. 1. As can be seen from FIG. 2 by looking into inlets 109 and 111,portions 113 and 115 of directional microphone cartridge 103 extendpartially into ducts 105 and 107, respectively, as mentioned above. Inother words, the inside volume of the sound passages created by ducts105 and 107 is formed in part by surfaces of the directional microphonecartridge 103. More specifically, the sound passage created by duct 105has an inside volume formed in part by a portion of top surface 117 anda portion of side surface 119 of directional microphone cartridge 103.Similarly, the sound passage created by duct 107 has an inside volumeformed in part by a portion of top surface 117 and a portion of sidesurface 121 of directional microphone cartridge 103.

Thus, in the configuration of FIGS. 1 and 2, the sound passages createdby the ducts have an inner volume formed by inside surfaces of the ductsand by surfaces of the directional microphone cartridge. Such aconfiguration enables the directional microphone assembly 101 to have asmaller overall length dimension than if the sound passages had insidevolumes formed only by inside surfaces of the sound ducts themselves.

FIG. 3 is a top view of the directional microphone assembly 101 of FIG.1 showing a restrictor 123 placed in a top portion of (front) sound duct105. The restrictor 123 may be inserted into inlet 109 of sound duct 105in a friction fit manner so that the restrictor 123 is flush with thetop surface 117 of the directional microphone cartridge 103. Of course,other placements of the restrictor 123 are also possible. The restrictor123 may be made of PVC tubing, for example, and may be used when it isdesired to increase the acoustical inertance of the sound passage formedby (front) sound duct 105.

FIG. 4 is a top view of the directional microphone assembly 101 showingacoustic dampers 125 and 127 placed in top portions of sound ducts 105and 107, respectively. The dampers 125 and 127 may also be inserted intoinlets 109 and 111, respectively, of sound ducts 105 and 107 in afriction fit manner.

FIG. 5 is a side view of the directional microphone assembly 101 of FIG.1 showing both the restrictor 123 and the acoustic dampers 125 and 127in an assembled relationship. As can be seen, restrictor 123 is locatedwithin an upper portion 129 of sound duct 105 so that it is flush withthe top surface 117 of directional microphone cartridge 103. Damper 125is also located within the upper portion 129 of sound duct 105 so thatit is flush with a top surface of restrictor 123. Damper 127 issimilarly located within an upper portion 131 of sound duct 107. Dampers125 and 127 may be cup-shaped, as shown, may be made of a wovenmesh-type material, such as metal, for example, and may have values of680 ohms and 680 ohms, for example. Of course, the dampers 125 and 127may be shaped differently, may be made of other types of material (e.g.,cloth or polyester), and may have different values and still fall withinthe scope of the present invention. In addition, the dampers 125 and 127may be placed in other locations, such as, for example, at the front andrear sound inlet ports or openings of directional microphone cartridge103, respectively.

FIG. 6 illustrates one embodiment of the directional microphonecartridge 103 of the directional microphone assembly of the presentinvention. A front sound inlet port or opening 129 is located at leastpartially on the side surface 119 of directional microphone cartridge103, and a rear inlet port or opening 131 is located at least partiallyon the side surface 121 of directional microphone cartridge 123. Thefront sound inlet port 129 may have a length dimension of approximately0.040 inches (1.02 mm) and a width dimension of approximately 0.010inches (0.25 mm), for example, and the rear sound inlet port 131 mayhave a length dimension of approximately 0.080 inches (2.03 mm) and awidth dimension of approximately 0.020 inches (0.51 mm), for example. Ofcourse, the front and rear sound inlet ports 129 and 131 may have otherdimensions and take on different shapes and still fall within the scopeof the present invention.

In any case, the front sound inlet port 129 enables the acousticalcoupling of sound to a front side of a diaphragm (not shown) located inthe directional microphone cartridge 103, and the rear sound inlet port131 likewise enables the acoustical coupling of sound to a rear side ofthat diaphragm. Upon assembly of a system such as directional microphoneassembly 101 described above, sound ducts 105 and 107 cover sound inletports 129 and 131, respectively, as explained more completely below.

Also as explained more completely below, directional microphonecartridge 103 includes three contacts 133, 135 and 137 for electricallyconnecting to an equalization circuit or other hearing aid circuitry,such as, for example, a hearing aid amplifier.

FIG. 7 illustrates one embodiment of a sound duct in accordance with thepresent invention. Sound duct 139 as shown in FIG. 7 is the same as thesound ducts 105 and 107 illustrated above with respect to directionalmicrophone assembly 101. As can be seen from the figures, sound duct 139has a top portion 141 having a generally circular cylindrical shape.Sound duct 139 also has a middle portion 143 having a cut-away area 145,such that middle portion 143 has only a semi-circular cylindrical shape.Finally, sound duct 139 further has a bottom portion 147 having apartial, non-circular sphere-like shape.

Sound duct 139 is mounted on a directional microphone cartridge, suchas, for example, directional microphone cartridge 103 discussed above,by fitting the cut-away portion 145 against the directional microphonecartridge. In other words, sound duct 139 has a mating surface 149 thatrests at least partially against the directional microphone cartridge.More specifically, a portion 151 of mating surface 149 rests on a topsurface of the directional microphone cartridge, a curved portion 153 ofmating surface 149 rests on a curved portion of the directionalmicrophone cartridge, and a further portion 155 of mating surface 149rests on a side surface of the directional microphone cartridge. Thus,the junction between the mating surface 149 of sound duct 139 and theouter surfaces of the directional microphone cartridge generally forms ashape on the outer surfaces of the directional microphone cartridge thatcompletely surrounds the sound port or opening located on the sidesurface of the directional microphone cartridge (see FIG. 8). Thus, onlysound entering inlet 157 is acoustically coupled to the diaphragm of thedirectional microphone cartridge.

Sound duct 139 may be attached to the directional microphone cartridgeby use of epoxy or other adhesive at the junction between the surface149 of the sound duct 139 and the relevant outer surfaces of thedirectional microphone cartridge. Once it is attached to the directionalmicrophone cartridge, the sound duct 139 creates a sound passage to theport in the cartridge having a volume formed by an inner surface of thesound duct 139 and outer surfaces of the directional microphonecartridge, as discussed above.

FIG. 8 illustrates additional detail regarding the mounting of soundduct 139 on a directional microphone cartridge.

While sound duct 139 is shown as having the shape generally describedabove with respect to FIG. 7, duct 139 may of course have other shapesand still fall within the scope of the present invention. For example,the sound duct of the present invention may generally have anon-circular cylindrical shape, such as rectangular. It also may have agenerally uniform radial dimension along its length, so that it has onlytwo portions defining its overall shape rather than the three portions(141, 143 and 147) discussed above with respect to sound duct 139 ofFIG. 7.

FIG. 9 illustrates another embodiment of a sound duct in accordance withthe present invention, having such a generally uniform radial dimensionalong its length. More specifically, sound duct 159 has a generallycircular cylindrical shape along its length, but for cut-away area 161.As can be seen, sound duct 159 has a top portion 163 having a generallycircular cylindrical shape, and a bottom portion 165 having only asemi-circular cylindrical shape. Thus, sound duct 159 has only twoportions 163 and 165 defining its overall shape, rather than the threeportions (141, 143 and 147) discussed above with respect to the shape ofsound duct 139 of FIG. 7.

Sound duct 159, like sound duct 139 of FIG. 7, is mounted on adirectional microphone cartridge, such as, for example, directionalmicrophone cartridge 103 discussed above, by fitting the cut-awayportion 161 against the directional microphone cartridge. Sound duct 159similarly has a mating surface 169 that rests at least partially againstthe directional microphone cartridge. A portion 171 of mating surface169 rests on a top surface of the directional microphone cartridge, acurved portion 173 of mating surface 169 rests on a curved portion ofthe directional microphone cartridge, and a further portion 175 ofmating surface 169 rests on a side surface of the directional microphonecartridge. Again, the junction between the mating surface 169 of soundduct 159 and the surfaces of the directional microphone cartridgegenerally forms a shape on the outer surfaces of the directionalmicrophone cartridge that completely surrounds the sound port or openinglocated on the side surface of the directional microphone cartridge.Only sound entering inlet 177 is acoustically coupled to the diaphragmof the directional microphone cartridge.

Similar to sound duct 139 of FIG. 7, sound duct 159 may be attached tothe directional microphone cartridge by use of epoxy or other adhesiveat the junction between the surface 169 of the sound duct 159 and therelevant outer surfaces of the directional microphone cartridge. Whenattached, the sound duct 159 likewise creates a sound passage to theport in the cartridge having a volume formed by an inner surface ofsound duct 159 and outer surfaces of the directional microphonecartridge, as discussed above. Sound duct 159 may be simply machinedfrom a circular, cylindrical tube, and may have dimensions similar tothose of sound duct 139.

FIG. 10 illustrates additional detail regarding the mounting of soundduct 159 on a directional microphone cartridge. If, for example, soundduct 159 is machined from a circular cylindrical tube as suggestedabove, plugs 179 may be used to close open bottom ends of the sound duct159. Plugs 179 may, for example, be press fit within the open bottomends of sound ducts 159, or may be attached to the open bottom ends ofsound ducts 159 using epoxy or other adhesive material.

While the sound ducts discussed above are shown to be components thatare separate and distinct from the directional microphone cartridge,they may also be formed as an integral part of the directionalmicrophone cartridge housing. For example, FIG. 11 illustrates adirectional microphone cartridge housing portion or half 181 havingsound duct portions 183 and 185 formed as an integral part of housingportion 181. FIG. 12 similarly illustrates another directionalmicrophone cartridge housing portion or half 191 housing sound ductportions 193 and 195 formed as an integral part of housing portion 191.

The housing portions 181 and 191 may be assembled by bringing themtogether until corresponding mating surfaces on housing portions 181 and191 engage to form a complete directional microphone cartridge housinghaving integrated sound ducts. FIG. 13 illustrates such an assemblytechnique. As can be seen, sound duct portion 183 of housing portion 181engages sound duct portion 193 of housing portion 191 to form onecomplete sound duct. Similarly, sound duct portion 185 of housingportion 181 engages sound duct portion 195 of housing portion 191 toform another complete sound duct.

FIG. 14 illustrates a completed assembly, in which housing portions 181and 191 are engaged to form a complete directional microphone cartridge197 having integrated sound ducts. Housing portions 181 and 191 may besnap-fit together or may be held together using epoxy or other adhesivematerial, for example. Of course, the housing portions and sound ductportions may take different shapes than as shown in FIGS. 11-14, so thatdifferent sound duct, cartridge housing, cartridge port, etc.,configurations may be implemented if desired.

FIG. 15 illustrates an alternate embodiment of a directional microphoneassembly of the present invention. Directional microphone assembly 201comprises a directional microphone cartridge 203 and a sound ductassembly 204. Sound duct assembly 204 may be formed from a single sheetof material, such as metal, for example. More specifically, a sheet ofmaterial is cut and shaped to create sound ducts 205 and 207, as well asmounting members 209, 211, 213 and 215. Another mounting member (notshown), corresponding to mounting member 215 adjacent sound duct 205, islikewise located adjacent sound duct 207.

During assembly, the directional microphone cartridge 203 is positionedbetween the sound ducts 205 and 207 of sound duct assembly 204, and themounting members (including mounting members 209, 211, 213 and 215) ofsound duct assembly 204 are wrapped around the directional microphonecartridge 203 to hold the sound ducts 205 and 207 in place. In otherwords, the sound duct assembly 204 “hugs” the directional microphonecartridge 203. Epoxy or other adhesive material, for example, may alsobe used to secure the sound duct assembly 204 with the directionalmicrophone cartridge.

FIG. 16 is another view of the directional microphone assembly of FIG.15. Similarly as discussed above with respect to FIG. 10, plugs 217 maybe used to close open bottom ends of the sound ducts 205 and 207 asshown. Again, plugs 217 may, for example, be press fit within the openbottom ends of sound ducts 205 and 207, or be attached to the openbottom ends of sound ducts 205 and 207 using epoxy or other adhesivematerial.

FIG. 17 illustrates a directional microphone assembly of the presentinvention having an equalization hybrid. Equalization may be used, ifdesired, to compensate for low frequency roll-off and to provide a flatresponse similar to that of an omnidirectional hearing aid microphone.Directional microphone assembly 221 may be generally the same asdirectional microphone assembly 101 discussed above, for example, withthe addition of an equalization hybrid 223 mounted on a side surface 225of directional microphone cartridge 227. Equalization hybrid 223includes three contacts 229, 231 and 233 for electrical connection withcontacts 235, 237 and 239, respectively, of the directional microphonecartridge 227, as shown. Equalization hybrid 223 also includes contacts241, 243 and 245 for electrical connection to hearing aid circuitry.

FIGS. 18A and 18B show exemplary details of the equalization hybrid 223.Hybrid 223 may have the dimensions and contact configurations as shownin FIGS. 18A and 18B.

FIG. 19 is a diagram illustrating an exemplary interconnection betweenthe directional microphone cartridge 227 and the equalization hybrid223. Equalization hybrid 223 includes, in addition to the contactsmentioned above with respect to FIGS. 17-18, an equalization die circuit247. The equalization hybrid 223 may be an ER-82 EQ Hybrid, and theequalization die circuit 247 may be an ER-81 Die, both from EtymoticResearch Inc.

FIG. 20 is a circuit diagram illustrating exemplary circuitry forimplementing equalization.

While FIG. 17 shows the equalization circuitry mounted on the outside ofthe directional microphone cartridge, equalization circuitry may insteadbe located within the directional microphone cartridge. FIG. 21illustrates a directional microphone cartridge having a larger housingvolume to accommodate internal equalization circuitry. Specifically,directional microphone cartridge 251 has a thickness dimension of 0.090inches (2.29 mm), for example, as shown in FIG. 21. Directionalmicrophone cartridge 103 of directional microphone assembly 101, bycomparison, has a thickness dimension of 0.069 inches (1.75 mm) (seeFIG. 2). The additional space in directional microphone cartridge 251 isused to carry equalization circuitry.

FIGS. 22 and 23 are side and perspective views, respectively, of adirectional microphone assembly having internal equalization circuitry.Directional microphone assembly 253 is generally thicker thandirectional microphone assembly 101 discussed above. The thicknessdifferential between directional microphone assembly 253 and directionalmicrophone assembly 101 may be seen by comparison of FIGS. 22 and 23 toFIGS. 2 and 8, for example.

FIG. 24 illustrates an in-the-ear hearing aid having a directionalmicrophone assembly mounted therein. The directional microphone assemblymay, for example, be that shown in FIG. 17. Hearing aid 261 comprises ashell 263 and a faceplate 265 mounted to the shell 263. Faceplate 265includes a battery door 267 as well as acoustic openings 269 and 271.Acoustic openings 269 and 271, which are shown as rectangular, may alsobe oval, circular, or any other shape. Acoustic openings, 269 and 271acoustically couple sound from the sound field through the faceplate 265to respective sound ducts of the directional microphone assembly.

Faceplate 265 also includes on its inner surface a pair of locatingwells 273 and 275 for receiving respective sound ducts of thedirectional microphone assembly. Upon assembly of the hearing aid, thesound ducts of the directional microphone assembly are respectivelyinserted into the locating wells 273 and 275. The sound ducts may bepress-fit into the wells, for example. Epoxy or other adhesive materialmay also be used to secure the directional microphone assembly to thefaceplate. Once the directional microphone assembly is secured andelectrically connected to hearing aid circuitry (not shown), thefaceplate 265 is then mounted to the shell 263 to form the completehearing aid 261.

FIG. 25 is an exploded view of the directional microphone assembly ofFIGS. 11-14, illustrating the internal components as well as thecartridge portions.

FIGS. 26A-G collectively illustrate a component by component assemblytechnique for the directional microphone assembly of FIGS. 11-14, usingthe components set forth in FIG. 25.

FIGS. 27A-G respectively illustrate the individual components set forthin FIG. 25.

FIG. 28 is a top view of an alternate embodiment of the directionalmicrophone assembly of the present invention, in which the sound ductsare offset from each other and relative to the center of the casehousing.

Many modifications and variations of the present invention are possiblein light of the above teachings. Thus, it is to be understood that,within the scope of the appended claims, the invention may be practicedotherwise than as described hereinabove.

1. A hearing aid comprising: a directional microphone assemblycomprising a housing having opposing side walls, the opposing sideswalls having opposing sound ducts formed thereon; and a directionalmicrophone cartridge comprising opposing side portions, wherein theopposing side portions of the directional microphone cartridge extend atleast partially into the opposing sound ducts of the opposing side wallsof the directional microphone assembly thereby reducing an overalldimension of the directional microphone assembly.
 2. The hearing aidaccording to claim 1, wherein the opposing side portions of thedirectional microphone cartridge have a first length therebetween, andthe opposing side walls of the directional microphone assembly have asecond length therebetween, and wherein the first length is longer thanthe second length.
 3. The hearing aid according to claim 1, wherein eachof the opposing sound ducts has an inside volume, and wherein at least aportion of at least one inside volume is formed by a surface of thedirectional microphone cartridge extending at least partially into aninterior of the opposing sound ducts.
 4. The hearing aid according toclaim 1, wherein each of the opposing sound ducts forms a sound passagehaving an inside volume formed at least in part by a portion of a topsurface and a portion of a side surface of the directional microphonecartridge extending into an interior of the opposing sound ducts.
 5. Thehearing aid according to claim 1, wherein at least one of the opposingsound ducts of the directional microphone assembly is adapted to receivea restrictor inserted therein, the restrictor and an interior of the atleast one of the opposing sound ducts having a frictional fittingrelationship, the restrictor being positioned flush with a top surfaceof the directional microphone cartridge within the at least one of theopposing sounds ducts, wherein the restrictor increases an acousticalinertance of a sound passage formed by the interior of the at least oneof the opposing sound ducts.
 6. The hearing aid according to claim 1,wherein the directional microphone assembly further comprises acousticdampers disposed in top portions of the opposing sound ducts, whereinthe acoustic dampers are inserted into inlets of the opposing soundducts in a frictional fit manner.
 7. The hearing aid according to claim1, wherein the directional microphone cartridge comprises anequalization circuit, the equalization circuit comprising a plurality ofelectrical contacts for operatively connecting the equalization circuitto additional hearing aid circuitry comprising a hearing aid amplifier.